It is often the case with a mechanically powered blade, such as the blade of a conventional rotary mower, that from time-to-time the edge of the blade will require sharpening. The sharpening of the blade edge increases the cutting efficiency of the blade by allowing the edge of the blade to cut the item intended instead of tearing the item as a blunt edge will do.
One problem with maintaining a sharp edge on such a blade is the inconvenience involved in removing the blade from its driving member in order to sharpen the blade on a blade sharpening device, such as, for example, a bench mounted grinding wheel. It would be better, therefore, to have a blade sharpening device which is portable and capable of use on the blade in-place, while the blade remains attached to its driving member.
There are many portable devices known. However there remains problems with such devices due to, inter alia, problems of safety, the ability to monitor the edge sharpening while it is in progress, and accuracy in controlling the angle of the edge being ground.
A list of prior patents which may be of interest is provided below:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,921,416 P. T. Shanahan 01/19/60 2,993,312 H. L. Holland et al 07/25/61 3,019,568 M. M. Sauers et al 02/06/62 3,122,865 H. W. Kolling 03/03/64 3,238,673 W. F. Thompson 03/08/66 3,648,414 W. F. Thompson 03/14/72 3,800,480 F. J. Keating 04/02/74 ______________________________________
U.S. Pat. No. 2,921,416 to Shanahan discloses a "lawn mower sharpener" in which a power drill is held up-side-down in a cradle-type holder driving a grinding wheel 23, in which the holder includes positioning extensions or protuberances 26 & 27 which directly contact the lawn mower blade 26 and bed plate 28, respectively, causing the device to be directly carried by the blade and its associated structure. Such a device is very limited in its application being confined to use basically only with the lawn mower design illustrated and can be relatively dangerous to use, with the rotating grinder being exposed to the user during use.
U.S. Pat. No. 2,993,312 to Holland et al discloses a blade sharpening device, which is completely hand manipulated. The sharpener is powered by a portable power tool, and has a wheel type grinding stone rigidly secured to a shaft and a frustro-conically shaped guide which is rotatably mounted on the shaft adjacent to the grinding stone. The shaft is connectable to the chuck of a portable power tool. The wheel and the frustro-conically shaped guide are arranged on the shaft with the smaller end of the guide adjacent to the wheel type stone to present a fixed angular grinding surface to a blade held against the guide. The device includes no guard for the rotating sharpening members, making it relatively dangerous, and no means are provided to allow the user to grasp the device at both ends, making it more difficult to use and accurately position.
U.S. Pat. No. 3,019,568 issued Feb. 6, 1962 to Sauers et al discloses a lawn mower grinder and sharpener for a reel type lawn mower in which the sharpener is braced (17/18) on one of the lawn mower's basic structural components, i.e. the spacer rod 15. As above, this approach of direct bracing on the lawn mower structure greatly limits the applicability and use of the device. Also, as above, the substantial exposure of the rotating sharpening device to the user makes the device relatively dangerous to use.
U.S. Pat. No. 3,122,865 issued Mar. 3, 1964, to Kolling discloses a power tool attachment for the sharpening of rotary mower blades. The attachment includes a guide that is spaced from the grinding surface and means for adjusting the spacing between the guide and the grinding surface by disassembling the sharpening device and removing a spacing element, thereby, allowing the use of an unused portion of the grinding surface when a portion of the grinding surface becomes worn. Like Holland et al, the Kolling device includes no guard for the rotating sharpening member, making it relatively dangerous to use, and no means are provided to allow the user to grasp the device at both ends, making it more difficult to use and accurately position.
U.S. Pat. No. 3,238,673 issued Mar. 8, 1966, to W. F. Thompson discloses a non-portable, blade sharpener having a rotary guide for maintaining the angle of the blade in relation to a rotating, flat, grinding surface, wherein the guide includes protrusions which cause the blade to move radially, in an upward and downward direction, against the rotating grinding surface. This patent is not directly relevant to the field of the invention and does not help to overcome the deficiencies of the prior art discussed above and below.
U.S. Pat. No. 3,648,414 issued Mar. 14, 1972 also to W. F. Thompson discloses a scissor-type blade sharpener and likewise is not directly relevant to the field of the invention and does not help to overcome the deficiencies of the prior art discussed above and below.
U.S. Pat. No. 3,800,480 issued Apr. 2, 1974, to Keating discloses a portable, on-site, in-place blade sharpener which includes an angular drive means mounted in a housing containing an enclosed, dedicated, electric motor, with the device being hand-manipulated by the user grasping the motor housing 14 by itself or in conjunction with the sharpener housing 19 and moving the device along the blade edge. The angular drive means is connected between the electric motor 21 and a grinding wheel 35 for coupling the rotational energy of the internal motor to the grinding wheel. Such an approach, in which the device rides through a guide plate 11 in flat-face-to-flat-face surface engagement with the underside of the blade and which does not use a multi-purpose electric drill but rather a contained, dedicated motor, is relatively inflexible in its use and relatively expensive. It does not provide freedom of lateral or angular movement, nor the easily controllable and strongly grippable handle of a power drill, all of which can assist in the easy and accurate positioning of the rotating sharpening member on the blade.
As will be understood from the discussions below, the present invention overcomes the above detailed deficiencies of the prior art and substantially improves upon the prior art by providing an on-site, in-place, portable blade sharpening device for lawn mower blades and the like using the standard type portable electric hand drill for power which device is hand-manipulated, adaptable for use with many different lawn mower designs, relatively safe in use, and easily, stably and accurately moved and positioned by the user using an easily maneuverable two-hand grasp at opposed ends of the combined device and drill.